This invention relates to microprocessor systems, and more particularly to interface circuits formicroprocessors.
In order to reduce the cost, size, power dissipation and complexity of a microprocessor system, it is usually preferable to include all of the circuitry of the system in a minimum number of integrated circuits. Indeed, for many small systems such as calculators, electronic games, and applicance controllers, all of the system can be in a single chip. For more complex systems, especially those involving analog signals such as speech, the cost of including the interface circuitry on the chip with the CPU becomes prohibitive. That is, very large high-performance processors can be built as single-chip devices, and most or all of the memory needed for the system can be included on this same chip; this is still a relatively low-cost device because the same device can be used for many different systems, allowing large scale production and minimum design effort. The interface circuitry for connecting this CPU to the remainder of the system may add disproportionately to the design cost and system cost, however, because the interface varies from system to system, requiring unique circuit design, chip design, packaging, board layout, and the like, and also resulting in more limited production runs, so economy of scale is not achieved.
It is the principal object of this invention to provide improved interface circuitry for microprocessor systems, more particularly to provide interface circuitry that is useful in a wide variety of systems and for different purposes without redesign. Another object is to provide peripheral I/O circuitry or interface circuitry for handling analog signals such as speech, particularly such circuitry which is programmable by the processor so that a variety of functions is available.